1. Field of the Invention
This invention relates to flash-spinning polymeric film-fibril strands. More particularly, the invention concerns an improvement in such a process which permits flash-spinning of polyethylene strands from a liquid medium which, if released to the atmosphere, Will contain a reduced amount of the trichlorofluoromethane (or "F-11") which has been implicated as a source of depletion of the earth's ozone.
2 Description of the Prior Art
Blades and White, U.S. Pat. No. 3,081,519, describes a flash-spinning process for producing plexifilamentary film-fibril strands from fiber-forming polymers. A solution of the polymer in a liquid, which is a non-solvent for the polymer at or below its normal boiling point, is extruded at a temperature above the normal boiling point of the liquid and at autogenous or higher pressure into a medium of lower temperature and substantially lower pressure. This flash-spinning causes the liquid to vaporize and thereby cool the exudate which forms a plexifilamentary film-fibril strand of the polymer. Preferred polymers include crystalline polyhydrocarbons such as polyethylene and preferred spinning liquids include halocarbons such as F-11
Although F-11 has been a very useful solvent for flash-spinning plexifilamentary film-fibril strands of polyethylene, and has been the solvent used in commercial manufacture of polyethylene plexifilamentary strands, the escape of such a halocarbon into the atmosphere has been implicated as a source of depletion of the earth's ozone. A general discussion of the ozone-depletion problem is presented, for example, by P. S. Zurer, "Search Intensifies for Alternatives to Ozone-Depleting Halocarbons", Chemical & Engineering News, pages 17-20 (Feb. 8, 1988).
An object of this invention is to provide a process for flash-spinning plexifilamentary film-fibril strands of fiber-forming polyethylene wherein the solvent contains a reduced amount of F-11 and the process can be operated without major apparatus modifications to a facility which was constructed for flash-spinning from F-11 alone.